The present invention relates to an even pressure welding method by using fluid pressure and for joining a plurality of joined members made of thermoplastic resin by fluid pressure to produce a flow path member having therein a fluid flow path.
Conventionally, there is a known method as shown in FIG. 5 as a method for producing a flow path member having a fluid flow path. In this method, after fluid flow paths formed of holes or grooves are formed by machining in junction faces A of a plurality of joined members 1 and 2 made of thermoplastic resin, the joined members 1 and 2 are closely fitted in a metal mold 3 with the members 1 and 2 joined to each other through the junction faces A, the mold is closed with the junction faces A pressed against each other to heat and soften the joined members 1 and 2, and the joined members 1 and 2 are welded through the junction faces A by using expanding force of the resin at this time.
In the above prior-art producing method, however, it is difficult to closely fit the joined members 1 and 2 in the metal mold 3 without a gap in welding the joined members 1 and 2 and it is impossible to restrain the joined members 1 and 2 in an isotropic manner. Therefore, the joined members 1 and 2 are not evenly pressurized and warps are generated in the joined members 1 and 2.
Because the joined members 1 and 2 cannot be restrained in the isotropic manner and the joined members 1 and 2 are pressurized by using expanding force of the resin, control of pressure in welding the joined members 1 and 2 is difficult.
Furthermore, because it is necessary to produce the metal mold 3, there is a problem of the large number of man-hours needed, which should be overcome.
It is an object of the present invention to provide an even pressure welding method by using fluid pressure, the method being able to suppress a warp in welding joined members, to facilitate control of pressure in welding, and to reduce the number of man-hours.
The above and other objects and novel features of the invention will become apparent from the description of the present specification and the accompanying drawings.
To achieve the above object, according to the invention, there is provided an even pressure welding method including the steps of: joining or layering a plurality of joined members each made of thermoplastic resin and having a fluid flow path formed of a groove and/or a hole in a junction face to each other with the fluid flow paths communicating with each other; vacuum-packing the joined members which have been joined to each other by housing the joined members in a wrapping having heat resistance, airtightness, and flexibility; heating a wrapped body obtained by the vacuum-packing to soften the joined members; welding the softened joined members to each other through the junction faces by applying fluid pressure to an entire outer periphery of the heated wrapping to evenly pressurize the wrapping from a periphery; and canceling the pressurization to cool the welded joined members.
According to the invention, because fluid is used as means for pressurizing the joined members, the joined members which have been joined can be evenly pressurized by the fluid from outside and reliably welded to each other, control of pressure in welding is easy, and it is possible to realize shortening of welding time and suppression of the warp in welding. Moreover, because it is unnecessary to produce a metal mold unlike the prior art, the number of man-hours can be reduced.
Furthermore, because the joined members are pressurized in a state in which the members are vacuum-packed, the pressurizing fluid used such as oil is prevented from adhering to the outer faces of the joined members, entering the groove and the hole of the joined members, and flowing between the junction faces of the joined members.
In the invention, a protecting plate for reinforcing the wrapping is preferably disposed between outer faces of the joined members in which the fluid flow paths open and the wrapping in vacuum-packing the joined members.
In the invention, the wrapped body may be heated by an oven and then immersed in and pressurized by the fluid in a pressure vessel or the pressurizing fluid may also function as heating means, the wrapped body may be immersed and heated in the pressurizing fluid, and then pressure of the pressurizing fluid may be increased to pressurize the wrapped body.
In the invention the joined members are preferably subjected to annealing so as to remove a warp due to heat in welding at a step of cooling the welded joined members.
The annealing is carried out in a reheating container such as an oven and an oil bath into which the joined members are moved from the pressure vessel or with the joined members immersed in the fluid in the pressure vessel by using the fluid as a heating medium.